This application relates to a method of easily testing the sensors in a dual sensor system to determine whether the sensors have failed, or are failing (i.e., only operating intermittently).
Modern vehicles are being provided with more systems which require sensor inputs. As an example, antilock brake systems utilize wheel speed sensor information from sensors associated with each of the wheels. The sensor information is often utilized to make critical decisions, such as whether and how much to actuate a brake. If the sensor information is inaccurate, this is of course, undesirable. If the sensors are not providing accurate information, it is important that the failure of a particular sensor be quickly identified. In the past, there have been no practical or simple methods for identifying a failing sensor in a two-sensor system.
Sensors can fail for a variety of reasons, and in a variety of ways. As an example, a sensor can become damaged such that is fails completely, or can become intermittent. This can occur due to damage, or manufacturing problems such as a bad solder joint. Further, environmental conditions can also cause a sensor to fail or become intermittent.
In this invention, a pair of sensors has their signals evaluated in a fashion to identify whether one of the sensors is failing or becoming intermittent. Typically, the sensors are of the sort which provides unitary signals in a cyclic fashion. There is preferably a phase angle difference between the two sensor signals. If a signal is sensed from a first sensor, and a second sensor which should be expected to provide a signal on the same cycle as the first signal, does not send a signal before the first sensor has a subsequent signal sent, the control identifies a problem. The signal can be sensed most preferably at the transition of either a rising or falling signal. If the sensors are operating correctly, then the sensor signals will be on relatively the same cycle, but spaced by some phase difference.
The present invention monitors transitions of the signals and maintains a memory of the last signal to transition. The system can then identify when one of the sensors has failed, or is becoming intermittent. Preferably, a counter associated without the control counts the number of signals from one of the sensors with a corresponding signal from the other. A preset number of signals can be set for determination that the other sensor has failed completely.
This system also incorporates a control that zeros the counter if there is a change in direction, as would otherwise potentially result in a signal being received from one of the sensors which had last sent a signal prior to the other sensor sending a signal. That is, for the wheel sensor, when the vehicle begins moving in a different direction (i.e., reverse to forward), it would be expected to receive two subsequent signals from one signal.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.